1. Field of the Invention
In a case where a time division multiple access communication network system via a plurality of transmission channels is used in a limited space, such as inside an automobile or a ship, the respective transmission channels are installed in the same place. A trouble (for example, damage on communication data resulting from the occurrence of a noise) is therefore highly likely to occur on a plurality of the transmission channels in the same place at the same time.
The present invention relates to a method for ensuring transmission and reception of data in a time division multiple access communication network system via a plurality of transmission channels under any circumstance.
2. Description of the Related Art
FIG. 11 is a view showing the configuration of a line switching system (network system) in the related art described in Japanese Patent No. 3908632 (Patent Document 1).
In the configuration of FIG. 11, the network system includes a plurality of communication nodes, all of which are interconnected via a duplex transmission channel: an active line and a spare line.
The term, communication nodes (also referred to simply as nodes), collectively means terminal devices and switching devices, which are components of the communication network.
In the line switching system (network system) of this configuration, each communication node normally transmits and receives data using the active line alone.
Upon detection of the occurrence of a trouble on the active line, a duplex switching device representing a line switching device continues communications by switching the transmission channel to the spare line.
As has been described, according to the line switching system (network system) in the related art shown in FIG. 11, even when communications are disabled due to the occurrence of a trouble on one of the transmission channels, it is possible for the transmission data to reach a receiver node via the other transmission channel by transmitting the data using a duplex transmission channel. Influences of the trouble to the overall network can be therefore lessened.
As another method, there is a method employed in a network shown in FIG. 12 and FIG. 13 in which communication nodes are interconnected in a ring shape via a plurality of transmission channels (for example, a duplex transmission channel).
FIG. 12 is a view showing the block configuration of each communication node of JP-A-9-36903 (Patent Document 2).
FIG. 13 is a view showing the configuration of a network of JP-A-9-36903 (Patent Document 2) in which communication nodes are interconnected in a ring shape.
The network includes a plurality of communication nodes, which are interconnected via a duplex transmission channel: a 0-system transmission channel and a 1-system transmission channel.
According to the ring-shaped network of this configuration, the respective communication nodes concurrently transmit the same data to the 0-system transmission channel and the 1-system transmission channel in the opposite directions at a time.
According to Patent Document 2, by transmitting the data in the manner described above, even when communications are disabled due to the occurrence of a trouble on one of the transmission channels (for example, the 0-system transmission channel), it is possible for the data to reach a receiver node by transmitting the data via the other transmission channel (for example, the 1-system transmission channel). Influences of the trouble can be therefore eliminated.
By employing the communication method in the ring-shaped network as described above in a bus-type network, which is a non-ring-shaped network shown in FIG. 14, it is readily anticipated that in a case where a trouble occurs on one transmission line, influences of the trouble can be eliminated by using data on the other transmission line that is being transmitted at the same time.
Herein, rings shown in FIG. 14 represent ring-type networks.
However, in order to transmit data via a duplex transmission channel using the method of Patent Document 1, transmission channels are switched after the detection of a trouble on one transmission line. Accordingly, the data being transmitted at the time of trouble detection fails to reach a receiver node because of the switching.
Meanwhile, in order to transmit data over the bus-type network via a duplex transmission channel using the method of Patent Document 2, a noise is generated on the both transmission channels in the same place. Moreover, the transmission data fails to reach a receiver node at the occurrence of a trouble, such as damage on the communication data.